1. Field of the Invention
The present invention generally relates to a synthetic resin pipe and, more particularly, to a synthetic resin pipe buried in the ground, or used inside or outside a building on the ground, or as a cable protecting pipe for protecting various types of wires and pipes
2. Background Description
Corrugated piping systems are generally known. These corrugated piping systems are typically formed of synthetic resin and include a pipe wall formed in an annularly or spirally uneven or corrugated shape. These corrugated piping systems are widely used as a cable protection pipe or a drainage pipe.
The conventional synthetic corrugated resin pipes have several drawbacks which are difficult to overcome. First, the stability of the pipes are poor when the synthetic corrugated resin pipes are plumbed. This is because the shape of the pipe is a circularly corrugated shape. Second, because of the circular shape of the synthetic corrugated resin pipes, it is difficult to arrange two or more such pipes in parallel to each other in their mutually adjoining positions. Because of this arrangement difficultly, when the pies are arranged under the ground dirt, sand and other debris easily enters between the respective pipes thus disturbing the straightness of the pipes. This, in turn, increases the insertion resistance when cables, such as electrical wires, are inserted through the pipes. Also, the resistance of a fluid may also easily increase because of the arrangement of the pipes.
Piping systems have been developed to solve the above problems of conventional corrugated pipes having circularly and unevenly corrugated shapes. FIGS. 11 to 13 show a pipe P.sub.1 having a cylindrical portion 2 having a substantially square cross section and a cylindrical portion 3 having a substantially circular cross section arranged alternately in the axial direction of the pipe.
Specifically, FIG. 11 shows the pipe P.sub.1, where the cylindrical portion 3 has a circular cross section of uniform thickness. Also, the cylindrical portion 2 has a square cross section having side portions 2b and a corner portions 2a, where the side portions 2b have a thicker cross section than the corner portions 2a. As better seen in FIGS. 12 and 13, the corner portions 2a have an intermediate portion A and corner portions B, B, where the two corner sections B, B are excessively decreased in thickness as compared to the intermediate portion A. As important, both thicknesses A, B are excessively decreased in thickness as compared to the thickness C of the central portions 2b. Because the corner sections B, B are excessively decreased in thickness, the corner sections B, B are extremely poor in pressure deformation resistance when compared with the remaining cylindrical portion 2, 3 and are thus easy to break.